The invention relates to an apparatus for cooling media or fluids, in particular charge air and recirculated exhaust gases in exhaust-gas recirculation systems, in particular for a motor vehicle or for large engines.
According to the prior art, turbochargers or other mechanical supercharging systems, such as compressors or the like, are used to increase the power of engines by compressing the air which is to be fed for combustion or the charge air. The fluid, gas or medium, such as in particular air, which is in the process heated as a result of the compression operation, is then generally cooled by a charge-air cooler. This is done also in order to further increase the air density and to limit the combustion peak temperatures. The charge air flows through a heat exchanger, which, by way of example, has ambient air or a cooling medium flowing through it and is thereby cooled. This allows the charge air to be cooled to a temperature which is approximately 20–90 K above the temperature of the ambient air or is as close as possible to this temperature.
In apparatuses with exhaust-gas recirculation, the exhaust gas is cooled in a dedicated heat exchanger and is then admixed or fed to the cooled charge air. This typically results in the temperature of the exhaust-gas/charge-air mixture being higher than the charge-air temperature at the outlet of the charge-air cooler.
This results in a significant drawback with regard to demands relating to reduced emissions, in particular of NOx, and reduced consumption, which are certain to rise in future.